Plunger clamps have been long known in the industry and act to provide a lever arm connected through a linkage to move a cylindrical plunger. The linkage generally consists of three pivot points all in the same plane as the motion of the plunger. Additionally, the linkage members all have substantially linear designs with longitudinal axes in line with the pivot points when the plunger is in either a push or pull position. An example of this type of device is manufactured by De-Sta-Co company, Model 604.
The design of such devices create problems. First, the mechanical advantage of the typical plunger clamp, that is, the correlation between the force applied to the handle and resulting reaction force to the plunger, is so great that the linkage is routinely over-stressed during normal use causing the linkage to fail.
Second, the linkage design of the typical plunger clamp uses rivets to make pivotal connections, routinely connecting only two members at a time. This type of connection has unbalanced forces resulting in a torquing force on the rivet. Accordingly, if the connected members of the plunger are not machined properly, within low tolerances, the stress on the rivets during normal use is increased to a level resulting in rivet failure.
Wherefore, it is an object of the present invention to provide a design of a plunger clamp having a mechanical advantage that does not over-stress the linkage during normal use.
Another object of the present invention is to provide a design of a plunger clamp with pivotal connections using full cross pins to lessen torquing forces at the pivotal connections, and thereby, preventing the failure of pivotal connections.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and the advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.